Hey Castelletti,
I recently purchased a pair of HD 650's from an Ebay seller (Razordog). Paid $359 + $5.95 shipping. So at least budget wise that would seem to fit your needs. This is actually my first experience with what I would consider high end headphones. I'm currently awaiting the delivery of a Crack/Speedball OTL and purchased these in anticipation of the new amp. My only use thus far of the 650's is through my laptop mostly listening to online radio (Pandora). I can't say I'm thrilled at the sound but there are a couple variables still in play. The convenience of having the phones at my desk definitely has me listening more. I'm also anticipating a significant increase in sound quality when I complete the new amp, but at this point I just have no idea how significant that may be. I'm currently listening to Jazz from the 50's and 60's. Miles Davis, Bill Evans, Herbie Hancock and many others. I don't stray too much but do enjoy many types of music. Currently listening to Antoine DuFour (Existence) and it sounds nice, just no wow factor......yet! The 650's are not of the noise canceling variety of phones as you may already know. This has a different tone than the canceling variety. Not sure how fellow audiophiles would compare these but it is something to consider. I also assume these phones will require some "break-in", which I can't detect much of yet. My best advise would be to try an listen to whatever you consider top contenders. That can be difficult I know. I would also suggest listening to a pair of HD 600's. Available for under $300 new and perhaps even less expensive at
http:/www.head-fi.orgor places similar. I hope this helps, good luck and enjoy that Jazz!
John